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FreeBSD-SA-09:06.ktimer                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Local privilege escalation

Category:       core
Module:         kern
Announced:      2009-03-23
Affects:        FreeBSD 7.x
Corrected:      2009-03-23 00:00:50 UTC (RELENG_7, 7.2-PRERELEASE)
                2009-03-23 00:00:50 UTC (RELENG_7_1, 7.1-RELEASE-p4)
                2009-03-23 00:00:50 UTC (RELENG_7_0, 7.0-RELEASE-p11)
CVE Name:       CVE-2009-1041

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

In FreeBSD 7.0, support was introduced for per-process timers as defined
in the POSIX realtime extensions.  This allows a process to have a limited
number of timers running at once, with various actions taken when each
timer reaches zero.

II.  Problem Description

An integer which specifies which timer a process wishes to operate upon is
not properly bounds-checked.

III. Impact

An unprivileged process can overwrite an arbitrary location in kernel
memory.  This could be used to change the user ID of the process (in order
to "become root"), to escape from a jail, or to bypass security mechanisms
in other ways.

IV.  Workaround

No workaround is available, but systems without untrusted local users are
not vulnerable.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE, or to the RELENG_7_1
or RELENG_7_0 security branch dated after the correction date.

2) To patch your present system:

The following patch has been verified to apply to FreeBSD 7.0 and 7.1
systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-09:06/ktimer.patch
# fetch http://security.FreeBSD.org/patches/SA-09:06/ktimer.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_7
  src/sys/kern/kern_time.c                                      1.142.2.3
RELENG_7_1
  src/UPDATING                                             1.507.2.13.2.7
  src/sys/conf/newvers.sh                                    1.72.2.9.2.8
  src/sys/kern/kern_time.c                                  1.142.2.2.2.2
RELENG_7_0
  src/UPDATING                                             1.507.2.3.2.15
  src/sys/conf/newvers.sh                                   1.72.2.5.2.15
  src/sys/kern/kern_time.c                                      1.142.4.1
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/7/                                                         r190301
releng/7.1/                                                       r190301
releng/7.0/                                                       r190301
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-1041

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-06:09.ktimer.asc
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